NGC 6940 & M103
Christopher A. Rice & Kaitlyn M. Smith

NGC 6940- Kaitlyn Smith

M103- Christopher Rice

NGC 6940 and M103 are known as star clusters, or open clusters. Star clusters are groups of stars that are tightly bound together by gravity. All of the stars in the clusters were created at the same time and therefore have the same amount of mass and lifespan. There are two types of star clusters: globular clusters and open clusters. One thing separates them is their lifespan. The life of an open cluster is shorter than that of a globular cluster due to the fact that open clusters contain less stars- usually containing less than one hundred stars, whereas globular clusters contain around a thousand or more. Because they have a small amount of stars, open clusters don’t have as much gravity working on them, which causes them to split away from each other.

NGC 6940 is an open star cluster that was discovered by William Herschel in 1784. It is found in the constellation Vulpecula the Fox and is estimated to be 2,510 light years away from the earth. It can be seen from both terrestrial spheres but it is lower in the southern hemisphere, with the exception of areas closer to the equator. The best time to locate this open cluster is in the evening during the months of June to November. NGC 6940 is slightly older than a billion years old, which is quite old for a star cluster. Because of it’s old age about twenty of NGC 6940’s sixty stars are red giants. NGC 6940 was estimated to last for 600 million years, but now it is 1.1 billion years are still here. This is rare for an open cluster because of the low gravity level introduced above.

M103 is an open cluster that is roughly 25 million years old, making it a baby on the scale of the universe. It is a part of the Cassiopeia constellation right next the star Ruchbar. M103 is one of the most distant star clusters at about 8,000 light years from earth. The diameter of this particular cluster is 14 light years, making it sizable compared to others. This cluster only has one red giant in it, meaning it still has many years to go.

NGC6940 and M103 are both open clusters, which attests to the grouping of both objects. As seen in both photos, open clusters are grouped together but only loosely. Both of these open clusters will die faster than any globular cluster would. There are not enough stars in these clusters to live for very long. The stars will slowly dissipate and the cluster will break up eventually. Just like M103, NGC6940 is composed of stars that are relatively the same age, because they were created at the same time.

So we’ve covered the similarities between the two clusters, now let’s cover the differences. For starters, the amount of stars in each cluster is different, but not by a lot. NGC 6940 contains 60 stars and M103 has 40- NGC 6940 also has twenty red giants, whereas M103 only has 1. You may recall from reading above that NGC 6940 is also older than M103, that would explain why it has more red giants than M103. They are also different distances from the Earth- M103 is approximately 8,000 light years away and NGC 6940 is only an estimated 2,510 light years away.